1. Field of the Invention
This invention relates to slide fasteners and particularly to woven slide fasteners employing polymer coupling elements molded on connecting threads and methods of manufacture.
2. Description of the Prior Art
The prior art, as exemplified in U.S. Pat. Nos. 3,328,857; 3,414,948; 3,445,915; 3,487,531 and 3,696,473, includes a number of slide fasteners employing polymer coupling elements molded on connecting threads wherein the coupling elements are initially molded in a flat condition and then the leg portions are folded together or toward each other; the attachment of such prior art coupling elements to the edge of the tape is either by threads such as stitching threads or warp threads passing over leg portions of the coupling elements or by threads such as weft threads passing around the connecting threads between the coupling elements. However, where conventional weaving apparatus and techniques are employed to secure such coupling element trains to the edge of the tape by looping the weft thread around the connecting threads, inferior slide fasteners have resulted due to (1) the connecting threads being shallowly embedded within the coupling elements and easily pulled out and thus providing insufficient support for the coupling elements against crosswise forces on the slide fastener, and (2) the coupling elements tending to rotate or twist relative to one another about an axis defined by the edge of the tape supporting the coupling elements since the connecting threads do not have sufficient rigidity to prevent such twisting which results in difficulty or failure in the coupling between opposite coupling elements of mating stringers. Reinforcement in the union between the coupling elements and the connecting threads has been previously suggested by welding the heel portions of the legs together adjacent to the connecting threads to thus embed the connecting threads centrally within the joined heel portions; but such welding requires additional apparatus and procedures increasing the cost of the slide fastener. The above U.S. Pat. No. 3,328,857 discloses sections of cord covered with molded plastic material in alternate and staggered spaces between legs to make the coupling elements more stable; however the problem of insufficient union between the coupling threads and the coupling elements is not overcome by such structure. Additionally the force required to open and close such prior art fasteners by moving the slider is sometimes excessively large and uneven.